1. Field of the Invention
The present invention relates to a pressure transmitter for use in a brake control system. The present invention further relates to a brake control system of the kind which is capable of controlling a braking force irrespective of a braking operation.
2. Disclosure Information
A brake control system of the aforementioned kind is disclosed in Japanese Patent Provisional Publication No. 62-149543. In such a brake control system, a pressure regulator and a pressure modulator are disposed between a master cylinder and each wheel cylinders. The pressure regulator is adapted to receive a master cylinder pressure and an additional pressure from a pressure source for producing a regulated pressure which is desired times larger than the master cylinder pressure. The pressure modulator outputs a braking pressure which is equal to the sum of the output pressure of the pressure regulator and the master cylinder pressure.
Such a prior art brake control system is disadvantageous since it is poor in responsiveness in a low braking pressure and high braking pressure variation frequency range. That is, the pressure modulator includes a piston slidable in a cylinder while defining an input pressure chamber and an output pressure chamber therewithin and sealing members installed on the piston to provide a seal between the piston and the cylinder. Due to this, in the event where a braking pressure which is low but high in variation frequency is supplied to the input pressure chamber of the pressure modulator, the piston remains immovable due to the friction between the cylinder and the sealing members, that is, the piston does not move until it is driven by a force prevailing against the friction between the cylinder and the sealing members. A hysteresis is thus caused between the output pressure increasing characteristic and the output pressure decreasing characteristic of the pressure modulator, thus deteriorating the responsiveness of the brake control system in a low braking pressure and high braking pressure variation frequency range, i.e., when the braking pressure is in a low range and its variation frequency is in a high range.